Multiple release mold coating

ABSTRACT

A method for molding articles where a composition is used to treat at least one shape determining face of a mold to impart durable release characteristics to said face which last through multiple molding cycles. The compositions comprise by weight 20 parts of primarily hydroxyl endblocked polydimethylsiloxane, 2 to 10 parts of alkyltriacetoxysilane, 20 to 80 parts of nonreactive organic solvent, and, optionally, 0.001 to 2 parts organometallic catalyst.

FIELD OF THE INVENTION

This invention relates to compositions used to treat the shapedetermining faces of molds to render the molds relatively nonadhesive tothe molded articles formed therein. The compositions used in the methodof the invention are comprised of primarily hyrdroxyl end-blockedpolydimethylsiloxane (I), alkyltriacetoxysilane cross-linker (II), andnonreactive organic solvent. Optionally, the compositions also comprisea condensation catalyst which decreases the time required to cure thefilm formed by the composition. The cured compositions are particularlyuseful in molding polyurethane foam articles by providing a nonreactivefilm on the surface of the shape determining portion of the mold thatallows the treated mold to release molded articles through multiplemolding cycles, and which does not defoam the surface of the moldedpolyurethane foam articles.

BACKGROUND OF THE INVENTION

One of the long recognized problems associated with molding articles isthe adhesion of the molded article to the mold upon completion of theform determining process. Adhesion between the molded article and molddecreases the efficiency of manufacturing molded articles by requiringmore force and time to remove the molded article from the mold. Oftenthe molded article is so tenaciously adhered that separation of thearticle from the mold damages the surface of the molded product.

While adhesion is not completely understood, at least two types ofadhesion can be identified which account for the adhesion of moldedarticles to molds. First, the process of molding intrinsically producesan intimate physical fit between the molded article and mold whichrequires some additional force to overcome. The second type of adhesionoccurs when chemically curing the molding material is part of themolding process. Quite often the chemicals involved in cure mechanismsare aggressive adhesives, for instance, in molding polyurethaneisocyanates are used as part of the resin forming process. Theseaggressive adhesives interact with the surface of the mold to form achemical bond between the mold and the molded article.

Both types of adhesion can be minimized. Where adhesion is mainlyattributable to the intimate physical contact between the molded articleand mold, a fluid or flexible material disposed between the mold andmolded article allows easier release of the article from the mold. Wherechemical adhesion is present, the provision of a chemically inert moldsurface decreases the chemical adhesion of the molded material to themold surface.

Cured and uncured organosilicon materials have been used for a number ofyears as mold release agents. Uncured silicone materials have been usedextensively in molding applications, but in the polyurethane foammolding applications such materials are undesirable because theytransfer into the polyurethane reagents, and defoam the polyurethanefoam.

Cured silicone compositions do not transfer into the molding materials,and are thus very useful in foam molding applications. However, manycured compositions do not adhere to the mold sufficiently to allow themold to be reused without recoating, or are not sufficiently hard toresist the abrasions which occur during the molding process. Oftenmaterials which provide sufficient abrasion resistance have been foundto cure so slowly that their application is impractical given theconstraints of typical manufacturing techniques. Other compositions havebeen found to interact with the molding composition in such a way thatthe mold release characteristics of the cured silicone compositionrapidly deteriorate.

U.S. Pat. No. 2,639,213 issued to Barth discloses the use of liquefiedgas in silicone based oil as a mold release agent. Like most uncuredsystems, this release agent will defoam molded foams as will the moldrelease agents containing silicone described in U.S. Pat. No. 2,811,408issued to Braley which describes a composition comprising a polysiloxaneresin, and a polysiloxane oil which is useful in molding organic andorganosilicon plastic articles.

U.S. Pat. No. 3,552,202 issued to Wada, et al. discloses a compositioncomprising αω hydroxyl end-blocked polydimethylsiloxane,polymethylhydrogensiloxane and polymethylphenylsiloxane. The mixture isclaimed to form a film upon application to a surface which providesnonsticky surfaces to sticky materials.

U.S. Pat. No. 3,492,394 issued to Heine illustrates the organic solventsolutions of perfluoroalkyltrialkoxy silane to form durable mold releasefilms. Heine speculates that the hydrolyzable groups react with theadventitious water and the mold surface to form a cured film.

U.S. Pat. No. 3,624,190 issued to Cekada, et al., discloses the use ofpolydimethylsiloxane fluid in conjunction with "typical release agents"to provide effective release coatings for polyurethane foam moldapplications. The polydimethylsiloxane fluid is not cured in thiscomposition, and its release into the molding reagent defoams certainpolyurethane formulations.

Oppliger, Canadian Pat. No. 624,114, teaches that cured films ofpolysiloxane oils or gums act as release coatings in polyurethane foammolding applications. Oppliger does not teach that these films givemultiple releases, and the examples and the compositions taught, andmaterials claimed in fact do not give multiple releases of moldedpolyurethane foam articles.

U.S. Pat. No. 3,634,764 issued to Brooks discloses a release coatingcomposition comprised of methyl-terminated polydimethylsiloxane,partially methoxylated polymethylpropylsiloxane resin, and curing agentsuch as tetraalkyltitinates or metal salts of carboxylic acids. Thepolydimethylsiloxane is not cured in this coating and intermixes withthe molded material. In polyurethane foam applications the uncuredpolydimethylsiloxane intermixes with the molding material, defoams thesurface of the molded article, and forms an undesirable skin.

U.S. Pat. No. 4,244,912 issued to Battice teaches that a compositioncomprised of vinyl end-blocked polydimethylsiloxane, vinyl groupcontaining polysiloxane resin, polymethylhydrogensiloxane cross-linkingagent, and a platinum containing hydrosilation catalyst is useful as amultiple release coating. This coating gives multiple releases of moldedpolyurethane foam articles, and does not defoam the surface of sucharticles. The coating is difficult to recoat, however, because the curesystem is inhibited by amines. Providing new cured coatings over spentcoatings is difficult to insure in practice.

U.S. Pat. No. 4,534,928 issued to Martin teaches multiple releasecoatings for polyurethane foam molding applications comprised ofpredominantly hydroxyl terminated polydimethylsiloxanes;trialkoxysilane; metal alkoxides; and nonreactive organic solvent. Thiscomposition is applied to a mold surface, the solvent is driven off, anda cured film is formed which has multiple release properties. Thecoating defoams the surface of certain formulations of polyurethane foammolded articles.

U.S. Pat. No. 3,579,469 issued to Grenoble discloses a paper releasecoating comprised of a silanol terminated siloxane gum; a silane of theformula, HSiX₃, where X is a hydrolyzable group; a metal salt of anorganic acid; and a nonreactive organic solvent. This composition is nottaught to be a mold release composition.

It is an object of this invention to provide an organosilicone coatingwhich permits multiple releases of molded articles between successiveapplications of the coating. It is also an object of the invention toprovide a mold coating which provides multiple releases of moldedpolyurethane foam articles. It is a further object of this invention toprovide mold release coatings which do not defoam the surface of moldedpolyurethane foam articles and which may be readily recoated. Finally,it is an object of the invention to provide a mold coating with multiplerelease characteristics in molded polyurethane foam applications whichcures to a nontacky state in less than ten minutes.

SUMMARY OF THE INVENTION

The present invention relates to a composition that is particularlyuseful in treating the shape determining portions of molds to renderthose portions nonadhesive to the articles molded thereby, whichcomposition comprises primarily α-ω dihydroxyl endblockedpolydimethylsiloxane, alkyltriacetoxysilane and nonreactive organicsolvent. The composition is useful in coating the inner surfaces ofmolds, and when cured imparts significant and durable releasecharacteristics to the mold. The cured coating is inert to the chemicalreactions used to make polyurethane foams, and, generally, does nottransfer into molding materials.

The compositions of the invention are easily cured with only moderatetemperatures being required to evaporate the nonreactive solvent fromthe compositions to form cured films. The resulting films providedurable release characteristics to the treated mold surfaces whichremains through multiple molding cycles. Therefore, molds treated withthe composition can be used several times before the surface of the moldneeds to be recoated.

The addition of catalysts to the composition decreases the time requiredto cure the films, and also produces films which are more abrasionresistant than the noncatalyzed composition films.

The molecular weight of the polydimethylsiloxanes used in thecomposition can vary widely. Polydimethylsiloxanes fluids with degreesof polymerization of about 25 can be used as well as high molecularweight polydimethylsiloxane gums. Mixtures of high and low molecularweight polymers are preferred.

In coating a mold with the composition the mold may be preheated beforethe composition is applied, or heated after application, in order toevaporate the organic solvent and form a cured resin film on the shapedetermining faces of the mold.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to novel compositions of curable organosilicon,and to the use of films formed by the curing of said compositions asmold release coatings. The compositions when used to coat shapedetermining surfaces of molds allow molded articles to be easily removedfrom the mold after completion of the molding process. The compositionsencompassed by the invention are comprised of primarily α-ω hydroxylend-blocked polydimethylsiloxanes; alkyltriacetsoxysilane; nonreactiveorganic solvent; and, optionally, a catalyst which promotespolymerization of the composition.

The polydimethylsiloxanes (I) of the composition are represented by thegeneral formula ##STR1## in which Y denotes a hydroxyl or a methylradical, but 80% of all Y groups are hydroxyl radicals, and k has anaverage value of at least about 25.

The polydimethylsiloxanes (I) of the composition are well knownhydroxylated siloxanes that can be prepared by conventional methods, forexample, by condensation polymerization of organosilanes.

The average chain length of the siloxane polymer is not critical as longit has an average degree of polymerization of at least about 25. Thereis no upper limit on the average number of siloxane units in the polymerchain. Nonflowable hydroxylated siloxane gums as well as hydroxylatedsiloxane fluids are encompassed within the description of the hydroxylendblocked polydimethylsiloxanes of the invention. However, fluids arepreferred over high molecular weight gums.

Mixtures of high molecular weight and low molecular weight hydroxylatedsiloxane polymers are also within the scope of the invention, and infact are the most preferred embodiment. A preferred mixture of siloxanepolymers contains a polymer of formula (I), which has an average kbetween 25 and 80, and a polymer also represented by formula (I) whichhas an average k between 300 and 1000. Preferably, the ratio of highmolecular weight polymer to low molecular weight polymer by weight isbetween about 0.1 and about 10. Most preferably, the high molecularweight polymer comprises at least two-thirds of the mixture, with about80 to 90 percent levels being optimal.

The alkyltriacetoxysilanes (II) used in the invention are of the generalformula RSi(OAc)₃ where R denotes a methyl, ethyl, or propyl radical,and OAc denotes an acetoxy radical. Preferably, mixtures ofethyltriacetoxysilane and methyltriacetoxysilane are employed in theinvention. These silanes are available commercially, and theirpreparation is known in the art.

The mold release compositions of this invention also contain an organicsolvent which serves to reduce the viscosity of the composition andfacilitate the application of the composition to the shape-determiningsurfaces of a mold. Solvents which are to some extent hydrophobic areadditionally advantageous because they facilitate the exclusion ofmoisture from the compositions and help prevent premature curing duringstorage.

Any organic solvent that is nonreactive with the other components of theinvention, and sufficiently volatile to evaporate rapidly when appliedto the mold surface can be employed in the invention. Generally, thepreferred solvents have normal boiling points below about 150° C. Thepreferred solvent for use in any particular molding operation willdepend on whether the mold release composition is applied to the moldsat room temperature, or at elevated temperatures. When room temperaturemolds are coated a lower boiling solvent is generally preferred. On theother hand, it is advantageous to use higher boiling solvents when themolds are coated at elevated temperatures.

The nonreactive organic solvent should be substantially water free toavoid premature curing of the composition. Preferred organic solventsinclude, for example, aliphatic hydrocarbons, cycloaliphatichydrocarbons, aromatic hydrocarbons and chlorinated hydrocarbons.Commercial mixtures such as white spirit, mineral spirits, and naphthaare also suitable. Further examples of useful solvents includecyclohexane, toluene, xylene, methylene chloride, methylene dichloride,ethylene dichloride, carbon tetrachloride, chloroform andperchloroethylene. Other solvents such as acetone, methylethylketone,ethyl acetate and tetrahydrofuran, and dioxane can also be used, but areless preferred because of their somewhat more hydrophilic character.

Since the solvent is nonreactive, it can be employed in the compositionsin essentially any proportion. Generally, it has been found thatcompositions containing at least about 50 percent by weight solvent areadvantageous because they are easy to apply to the mold surfaces andprovide films of the appropriate thickness with good permanence.

For the purposes of this invention the curing catalyst, when employed,can be any of those condensation catalysts that decrease the timerequired to cure the mixture of the hydroxyl end-blockedpolydimethylsiloxane and the alkyltriacetoxysilane cross-linker.

Such condensation catalysts include organometallic materials like thecarboxylic acid salts of metals such as tin, manganese, iron, cobalt,nickel, lead, and the like, or titinates such as alkyl titinates,acyltitinates, or the corresponding zirconates. The catalysts preferablyemployed in the invention are the tin salts of carboxylic acids, or themercapto tin salts. In particular, these catalysts include, but are notlimited to, dibutyltindiacetate, dibutyltindilaurate,dibutyltindioctoate, stannous octoate, dimethyl-tindineodeconoate,di-N-octyltin-S,S-di-iso-octylmercapto acetate,dibutyltin-S,S-dimethylmercapto acetate, or diethyltin-S,S-dibutylmercapto acetate. The catalysts can be incorporated into theinvention compositions in between 0.01 to 2 parts by weight to 100 partsof (I) and (II).

The proportions of hydroxyl end-blocked siloxane polymer (I), silane(II), and catalyst vary widely. The compositions without catalystspreferably have alkyltriacetoxysilane to polymer ratios of at least 1:5by weight. Higher ratios of silane to polymer improve the releasecharacteristics of the cured films. Even compositions with equal partsby weight of alkyltriacetoxysilane to siloxane polymer gave multiplereleases of polyurethane foam articles.

Compositions without catalyst produce tacky films when baked for about 5minutes at 100° F. However, these tacky films give multiple releases ofmolded polyurethane foam articles when at least a certain proportion ofalkyltriacetoxysilane to siloxane polymer exists. In general, films madefrom compositions with alkyltriacetoxysilane to siloxane polymer ratiosgreater than 1:5 were preferred when no catalyst is present in thecomposition.

In compositions with catalyst the proportion of (II) to (I) can be lowerthan the proportions used in the noncatalyst compositions. As little as1 part of the silane cross-linker (II) can be used per 20 parts of aprimarily hydroxyl endblocked polydimethylsiloxane mixture of highmolecular weight polymer and low molecular weight polymer to provide amultiple release coating.

The catalyst decreases the time required to cure the composition to anontacky film. Compositions without catalyst remain tacky for extendedperiods, while catalyst containing compositions cure in less than fiveminutes on molds surfaces heated to about 100° F. The cured catalystcontaining films were also more abrasion resistant than the curednoncatalyzed compositions, and gave more releases than the noncatalyzedcoatings with the same level of alkyltriacetoxysilane.

A preferred composition comprises 11.3 parts of a hydroxyl end-blockeddimethylsiloxane polymer with an average molecular weight of about28,000; 2 parts of a hydroxyl end-blocked dimethylsiloxane polymer withan average molecular weight of about 2,000; 6.7 parts of a 50:50 mixtureof ethyltriacetoxysilane and methyltriacetoxysilane; 0.1 partdibutyltindiacetate; and 80 parts naptha solvent.

The preferred compositions cure rapidly to form nontacky films uponapplication to heated mold surfaces. The resulting films allow the moldsto be reused several times before recoating is necessary. Moldedpolyurethane foam articles produced using molds treated with thepreferred compositions have smooth surfaces which show no evidence ofdefoaming.

The compositions may also include components which do not interfere withfilm formation. For instance, a colorant could be added to thecomposition to indicate where the composition had been applied.

The compositions can be prepared by mixing the siloxane polymer with thenonreactive organic solvent. The alkyltriacetoxysilane is then added tothis solution. The alkyltriacetoxysilane may be added to the nonreactiveorganic solvent, and then mixed with the siloxane polymer. The catalystis added to the siloxane polymer because of limited solubility of thecatalyst in many organic solvents, but it is not essential that thecomposition be made in this precise manner.

All of the components should be free of water, however, no extraordinaryprecautions need be taken. Typically, all that is required is that theorganic solvent be relatively water free. The large excess ofalkyltriacetoxysilane stabilizes the composition to the presence ofminute quantities of water and obviates the need for using specialequipment.

The nature of the products formed by curing the composition is notprecisely known, but it is believed that the silane acts as across-linker by reacting with the terminal hydroxyl radicals of thepolysiloxane. In the presence of water further hydrolysis andcondensation occurs forming a resin with the elimination of acetic acid.It is not clear what the role of the excess silane is, but the excess isnecessary to impart release characteristics to the film. The precedingdiscussion should not be understood as limiting the scope of theinvention to these proposed reactions.

The composition is stable when mixed with solvent, particularly thecomposition without a catalyst, and can be stored for extended periodsbefore being used. The composition can be applied to mold surfaces byany suitable means such as spraying, brushing, dipping, or rolling.After application the composition should be cured by heating in thepresence of atmospheric moisture and the organic solvent allowed toevaporate. The resulting film has release characteristics even whilestill tacky.

The composition can be used to coat molds in a variety of moldingapplications including polyurethane foam wherein the isocyanate used inthe polyurethane foam is chosen from the group consisting of methylenediphenyl isocyanates (MDI), tolylenediisocyanates (TDI), or polymericisocyanates (PMDI), as well as other chemically cured molding materialapplications.

EXAMPLES

The following examples are illustrative of the invention and should notbe construed as being an exhaustive list of the embodiments of theinvention. For this disclosure all viscosities were measured at 25° C.,and all parts, ratios, and percentages are reported by weight.

EXAMPLE 1

This example illustrates the importance of using a sufficient proportionof alkyltriacetoxysilane cross-linker to hydroxyl end-blockedpolydimethylsiloxane.

The following table summarizes the effect of the proportion of silane onthe cured compositions multiple release capabilities. In the first twoExamples, A and A1, 20 g of hydroxyl end-blocked polydimethylsiloxanewith a viscosity of about 2,000 centistokes (equivalent to a degree ofpolymerization of about 300) were mixed with the indicated amount ofalkyltriacetoxysilane (equal parts by weight of methyl- andethyl-triacetoxysilane), and 85 parts of methylene chloride. Thismixture was sprayed on the interior of a hot (140° F.) aluminum box moldand allowed to cure at the indicated conditions. Polyurethane moldingmaterial of a commercially used formulation was placed in the treatedmold and the mixture was allowed to foam cure at 140° F. for 5-8minutes. The molded article was removed and the mold was reusedrepeatedly until the molded article could not be removed, or showedsurface defects.

Samples B, B1 and B2 were made by mixing 20 g of a mixture, comprised of17 parts of a hyrdroxyl end-blocked polydimethylsiloxane with an averagemolecular weight of about 28,000 and 3 parts of a hydroxyl end-blockedpolymer with an average molecular weight of about 2,000, with the amountof alkyltriacetoxysilane (x-linker) indicated in Table 1 below, and 85 gof methylene chloride. The alkyltriacetoxysilane mixture comprised equalweights of ethyl- and methyl- triacetoxysilane.

This mixture was applied to the shape determining faces of an aluminumbox mold and allowed to cure at the indicated conditions.

                  TABLE 1                                                         ______________________________________                                                                   Time  Temp. No.                                    Sample Wt. Polymer                                                                              x-Linker Cured Cured Releases                               ______________________________________                                        A      20 g        1 g     30    140° F.                                                                       0                                     A1     20 g       10 g     15    140° F.                                                                      14                                     B      20 g       10 g     05    100° F.                                                                      25                                     B1     20 g       15 g     05    100° F.                                                                      30                                     B2     20 g       20 g     05    100° F.                                                                      32                                     ______________________________________                                    

The films were cured at the temperatures for the times indicated in thetable. Samples A1, B, B1, and B2 recoated the mold and gave multiplerelease characteristics to the recoated mold. Sample A, having ax-linker/polymer wt. ratio of less than 0.2 and no catalyst gave noreleases while those samples (A1, B, B1 and B2) having x-linker/polymerratios greater than 0.2 gave multiple releases.

EXAMPLE 2

The effect of using a condensation catalyst on the multiple releasecharacteristics of a cured film of the invention is illustrated by thisexample. A 15 g portion of a mixture used in Sample B of Example 1 wasmixed with 25 g of naptha solvent indicated in the table. Portions ofthe compositions were applied to a hot aluminum mold, and cured. Themolds were then used to mold polyurethane foam articles using acommercially employed formulation. The cured films gave multiplereleases of the molded polyurethane foam articles. The results aresummarized in Table 2.

                  TABLE 2                                                         ______________________________________                                        TACK FREE TIME WITH CATALYST                                                  Polymer                                                                              Silane  Tack Free Time                                                                             % Catalyst                                                                            No. Releases                              ______________________________________                                        20 g   10 g    --           0       27                                        20 g   10 g      5 minutes  0.03    27                                        20 g   10 g    3.5 minutes  0.1     43                                        ______________________________________                                    

At a catalyst concentration of 0.03% significant multiple releasecharacteristics were observed. Tack free time is the time required afterapplication to the mold surface before the coating is no longer tacky.Nontacky films are less susceptible to abrasions and are preferred whereabrasion resistance is important in the molding application.

EXAMPLE 3

The effect of silane to polymer ratio using condensation catalysts isillustrated in this example. 20 g of the polymer blend used in SamplesB, B1 and B2 of Example 1, and the indicated amount of thealkyltriacetoxysilane mixture of Example 1 were mixed with 80 g ofnaptha solvent and the condensation catalyst dimethyltindineodeconoate,and a portion of the mixture was applied to the shape determining facesof an aluminum box mold. Polyurethane molding material was placed in thetreated mold and foam cured at 140° F. for 5 to 8 minutes.

                  TABLE 3                                                         ______________________________________                                        Polymer  Silane   Tack Free Time                                                                              No. Releases                                  ______________________________________                                        20 g     2.5    g     0.75   min.   37                                        20 g     5      g     2.5    min.   47                                        20 g     10     g     3.5    min.   43                                        20 g     15     g     4      min.   35                                        ______________________________________                                    

All samples had 0.1% by total solids weight of the condensationcatalyst.

EXAMPLE 4

The average molecular weight of the siloxane polymer used in thecompositions effects the release characteristics of the films formedfrom the compositions. The following table shows that low viscosityfluids to gum-like polymers can be used in the compositions used in theinvention to form films which have multiple release characteristics. 20g of polydimethylsiloxane polymer, 10 g alkyltriacetoxysilane, and 80 gof solvent were mixed and a portion of the mixture was applied to theshape determining surface of a mold. The treated mold was used to moldpolyurethane foam articles. All of the films gave multiple releases ofmolded polyurethane articles as shown in the table below.

                  TABLE 4                                                         ______________________________________                                        Viscosity v. Releases                                                         Siloxane Polymer Viscosity                                                                       No. of Releases                                            ______________________________________                                        2,000 centistokes  14                                                         54-61 mils plasticity                                                                             3                                                         (ASTM D926)                                                                   ______________________________________                                    

EXAMPLE 5

Other compositions were made to compare the release characteristics ofthese materials to the materials encompassed by the invention.

(A) 20 g of a 2,000 centistoke α-ω hydroxyl end-blockedpolydimethylsiloxane was mixed with a stoichiometric excess (1 g) of thealkyltriacetoxysilane mixture described in Example 1, and diluted withmethylene chloride. The solution was sprayed on an aluminum mold at 140°F. After 30 minutes the mixture was still uncured and did not releasemolded polyurethane foam articles which had been foam cured at 180° F.for 5-8 minutes in the coated mold.

(B) 20 g of a high molecular weight, α-ω hydroxyl end-blockedpolydimethylsiloxane gum, a stoichiometric excess ofalkyltriacetoxysilane (1 g), and 80 g of methylene chloride were mixed.The solution was applied to an aluminum mold in a thin layer at 140° F.After 30 minutes the resulting film was still uncured. The treated molddid not exhibit release characteristics when employed in polyurethanefoam molding applications.

(C) 8 g of the gum used in Example 5c, which had a viscosity of about 60mils, 2 g of ethylpolysilicate, 0.1 gram of dibutyltindiacetate employedto promote rapid curing, and methylene chloride were mixed and a smallportion of the mixture was applied in a thin layer to the surface of analuminum mold at 140° F. After 15 minutes the mixture had cured on thesurface of the mold. The mold released cured polyurethane foam articles,but defoamed the surface of the articles.

(D) A mixture was prepared comprised of 9.7 g of α-ω hydroxylend-blocked polydimethylsiloxane with an intrinsic viscosity of 2,000centistokes, 0.3 gram of a methylhydrogensiloxane of the general formula##STR2## with a viscosity of about 30 to 40 centistokes, 0.1 gramdibutyltindioctoate, and methylene chloride. The mixture was applied asa thin coating on the face of an aluminum mold and cured at 140° F. for15 minutes.

The treated mold severely defoamed molded polyurethane foam articlesproduced by the mold.

(E) D was repeated using a polydimethylsiloxane gum instead of thefluid. A mold treated with the cured composition gave three releases.

(F) 13.3 g of the polymer blend of Sample B, Example 1, and 6.7 g ofmethyltrimethoxysilane, and 0.6 g of tetraoctyltitinate were mixed with80 g of naptha solvent. A thin coating of this mixture was cured for 15minutes at 140° F. The treated mold defoamed molded polyurethane foamarticles.

EXAMPLE 6

The composition used in Example 3 which contained 5 g of thealkyltriacetoxysilane was used to treat a tire mold. The treated moldreleased tires cured in the mold several times before the mold requiredretreatment.

What is claimed is:
 1. A method for making molded articles whichcomprises coating at least one shape determining face of a mold with acomposition comprising; (I) polydimethylsiloxane of the formula ##STR3##where Y is a methyl or hydroxyl radical with at least 80% of all Y beinghydroxyl, and k has an average value of at least about 25;(II)alkyltriacetoxysilane where the alkyl group is methyl, ethyl, or propyl,and; (III) a nonreactive organic solvent, and (I) is present in about 5to 20 parts by weight, (II) is present in about 1 to 20 parts by weight,and (III) is present in at least about equal parts by weight of thetotal weight of (I) and (II) combined, and the ratio of (II) to (I) byweight is at least 0.2;curing said composition placing molding materialin the mold; converting the molding material into a molded article; andremoving the molded article from the mold.
 2. The method of claim 1wherein the composition additionally comprises a condensation catalyst(IV).
 3. The method of claim 1 wherein the polydimethylsiloxane (I) ofthe composition is a mixture of polydimethylsiloxane polymerscomprising;(A) polydimethylsiloxane with an average k between about 25and 80; and (B) polydimethylsiloxane with an average k between about 300and
 1000. 4. The method of claim 3 wherein the composition alsocomprises a condensation catalyst (IV).
 5. The method of claim 3 whereinthe ratio of (A) to (B) by weight is between about 0.1 and
 10. 6. Themethod of claim 4 wherein the ratio of (A) to (B) by weight is betweenabout 0.1 and
 10. 7. The method of claim 6 wherein thealkyltriacetoxysilane (II) in the composition is a mixture ofmethyltriacetoxysilane and ethyltriacetoxysilane in about equal parts byweight.
 8. The method of claim 7 where the condensation catalyst ischosen from the group consisting of dibutyltindiacetate,dibutyltindilaurate, dibutyltindioctoate, dimethyltindineodeconoate,stannous octoate, di-N-octyltin-S,S-di-iso-octyl mercapto acetate,dibutyltin-S,S-dimethylmercapto acetate, ordiethyltin-S,S-dibutylmercapto acetate, and is present in about 0.01 to2.0 parts by weight to 100 parts by weight of the total of (I) and (II).9. The method of claim 8 wherein the molded article is made of apolyurethane foam and wherein the isocyanate used in molding material isselected from the group consisting of methylenediphenylisocyanates(MDI), tolylenediisocyanates (TDI), or polymeric isocyanates (PMDI). 10.A method for making molded articles which comprises coating at least oneshape determining face of a mold with a composition comprising;(I) amixture of a high molecular weight polydimethylsiloxane and a lowmolecular weight polydimethylsiloxane, both of the formula ##STR4##where Y is a methyl or hydroxyl radical with at least 80% of all Y beinghydroxyl, the low molecular weight polydimethylsiloxane (A) has a valueof k between 25 and 80, the high molecular weight polydimethylsiloxane(B) has an average value of k between about 300 and 1000, and the weightratio of (A) to (B) is less than 0.5; (II) alkyltriacetoxysilane wherethe alkyl group is methyl, ethyl, or propyl, and; (III) a nonreactiveorganic solvent, (IV) a condensation catalyst which decreases the timerequired to cure the composition in the presence of water; and (I) ispresent in about 5 to 20 parts by weight, (II) is present in about 1 to20 parts by weight, and (III) is present in at least about equal partsby weight of the total weight of (I) and (II) combined;curing saidcomposition; placing molding material in the mold; and, removing themolded article from the mold.
 11. The method of claim 10 wherein theweight ratio of (II) to (I) is at least 0.1.